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I have had only 5mm chain clearance with the 180/55 Q2. My chain adjustment had to be exact to get alignment and adequate chain clearance. I get more than twice that with with the Pirelli Rosso Corsas. The Q2s really flare out at the edge with a more angled out side wall. Same bike same 5.5 inch rim. Different tyre companies approach to design/construction I guess.
Its true too about using 190/55s.